Conventionally, a technology is well-known in which, instead of fixed assignment of a logical storage area available to a computer, a virtual volume which is a virtual logical storage area including the storage capacity available to the maximum limit is specified, and by assigning the required physical storage area each time the computer requires, the storage capacity of the storage device which provides the logical storage area is efficiently utilized. This technology is generally referred to as Thin Provisioning or by other terms.
For example, in the Patent Literature 1, for a virtual volume assigned to a higher-level device (host) by the Thin Provisioning technology, the configuration is proposed in which, by discarding an actual storage area assigned to the virtual volume (hereinafter, the unit of assigning the storage area from this actual storage area to the virtual volume is referred to as a “page” (unit physical storage area)) and making the same available to the other virtual volumes, the actual storage area is efficiently utilized. That is, by specifying a page desired to be discarded from the host and issuing a discard command to the page (address), the storage apparatus is made to perform the discard processing of the relevant page.